Oil/water separation treatment of oily wastewater within a separator tank by its exposure to plate stacks is already well known, as well as in-situ cleaning of such plate stacks involving emergence of pressurized air from an air sparging array below the plate stacks for dispersion of a bio-emulsifier cleaning agent introduced into the separator tank as disclosed in U.S. Pat. No. 6,659,290 B1 to Lawson et al. The cleaning process heretofore involved use of personnel under high workload conditions because of required repetition of the process. Also personnel were exposed to hazardous material during mixing of the cleaning agent with water before introduction into the separator tank. It is therefore an important object of the present invention to provide for in-situ cleaning of such oil/water separator tanks with reduced personnel workload and less exposure to hazardous material.